I have been told that, in order to charge my car’s battery fully, I should put it on a charger weekly. Supposedly, my electrical system only gives it a “superficial charge,” not a “deep charge.” That sounds to me like BS. Is it?
Also, folks say that if you leave a car battery on a concrete floor the concrete will suck all the charge out of it. Okay, I can imagine no mechanism for this to happen to a battery with an intact housing on a dry floor though I will give the benefit of the doubt to 1920-vintage batteries with hard rubber cases on moist concrete floors since I wasn’t around in 1920. And, though I am around today, it hardly seems worth the effort to test modern batteries when the theory is patent BS and I have you folks to ask, anyway. So, is it really as big a load of dung as it sounds?
dropzone let me help you out here.
The electrical system on a modern car is designed to keep a fully charged battery fully charged, or to recharge an almost fully charged battery. It will not fully charge an almost empty battery. So assuming that the battery in your car was fully charged, or almost so (a fair assumption) then under normal operating conditions the battery will remain fully charged. There are a couple of exceptions to this. First off in a very cold climate where it takes excessive cranking to start the car, lots of short trips could results in a depleted battery. Secondly, if a modern car is parked for an extended time, or not driven very often the parasitic draw of the computers can drag the battery down to the point where the car’s electrical system might not recharge it properly. On the cars I teach on we are talking about a period of a month or more. Cars driven daily or once a week do not have that problem. If a car that is driven normally does not keep a battery charged, the either there is a problem with the battery, the charging system, or there is an unexpected draw on the system (like the glove box light remaining on)
As for your second question, yes you are correct about rubber-cased batteries. Rubber cased batteries were in use up until the mid 60’s. (I can recall working on cars that had them when I was a wee young mechanic back in 1968) Anyway the there are two problems with concrete floors, both of which still exist to some degree. First off the rubber-cased batteries as they aged would gather dirt and grime on the top and sides of the batteries. This grime is will conduct electricity. Placing the battery on the concrete floor will then give a path to ground, and the battery will self discharge over time. While batteries still can get grimy the plastic cases don’t trap the grime the way tar topped batteries did. The second problem, which still exists, is that concrete floors are in general cold. Usually they are the coldest part of the room. Battery performance drops off big time with temperature. This is due to the chemical reaction inside the battery slowing down. IIRC if you assume a battery at 70F is 100% at 32F you are down to about 40% capacity. So if you take a fully charged battery out of a car, and place it on a cold floor for a while then put it back into the car, it will appear to have discharged from the reduced temp. In a cold climate I could even see this getting to the point of a no start condition. Even here in California I always put a battery out of the car on a couple of pieces of wood to keep the temp of the battery warmer. ::: Shrugs ::: Maybe I’m just a belt and suspenders kind of guy.
Those terms aren’t normally used in the automotive field. I suspect it’s some amateur’s way of trying to differentiate between the limited charging ability of the car’s alternator and the greater charging ability of an actual battery charger.
As Rick said, the alternator is not up to the task of recharging a significantly depleted battery–for that, you need the charger. But where someone got the idea that a properly working car needs its battery put on a charger weekly is beyond me.
If the floor temperature is much colder than the air temperature, then the voltage/cell will decrease (as stated by rick). But this usually isn’t a problem, unless the floor is so cold that that battery can’t turn over the engine in your car. (My car starts fine at 0 °F.) In my opinion, the absolute battery temperature is not as important as the temperature uniformity within the battery. As long as the battery doesn’t have a large temperature gradient in the vertical direction you’ll be O.K., even at fairly low temperatures. A large vertical temperature gradient could (theoretically) create circular electrical currents inside the battery, expending energy and thereby discharge the battery. This is because, in each cell, V[sub]OC[/sub] in the cold area will be lower than V[sub]OC[/sub] in the warm area. This creates current.
** Crafter_Man the senario I was thinking of goes something like this.
Guy is trying to get his car started in Winter in his garage (located in a cold climate) During the attempts to start the car the battery gets drug down to about 50% charge. This is when the air temp in the garage is about 60 degrees. At this point our intrepid mechanic decides that some serious work needs to be done to the engine. The battery is removed and set on a very cold cement floor. Cold snap hits town. One week later when the battery is re-installed the internal temp is somewhere between 0 and 32F. Now becasue the engine was apart the car takes some additional cranking and the battery can’t do it as there is not enough capicity left to crank the engine. Then our intrepid Bubba tells his buddies that the concrete floor discharged his battery.
NO, that is not true, the battery is cold, and you put it away not fully charged. But blaming the floor is so much easier.
This doesn’t work. Discharging a battery over time will happen if there’s a path from one battery terminal to the other, not if there’s a path to ground. You can attach a wire straight to one terminal of a battery and plug it directly into the ground, and nothing will happen so long as you leave the other battery terminal unconnected.
If the grime explanation was correct, the self-discharge would take place regardless of wether the battery was placed on the ground or not - as the discharge path between the positive and negative battery terminals would be present in either case.